Many electronic applications require patterned metallization of nonconductive substrates for interconnection among electronic devices. Examples of such applications include high-density packaging (multi-chip modules), antennas, flex circuits, printed wiring boards, and flat panel displays.
Radio Frequency Identification (RFID) is a type of automatic identification system. The purpose of an RFID system is to enable data to be transmitted by a portable device, called a tag, which is read by an RFID reader and processed according to the needs of a particular application. A basic RFID system consist of three components:
An antenna or coil
A transceiver (with decoder)
A transponder (RF tag) electronically programmed with unique information
Wireless articles, including tags, identification badges, smart cards, etc., are in wireless communication with a base unit or reader via a radio-frequency (RF) communication link. These articles can be used for electronic identification and tracking of articles, persons and transactions. RF transmissions transmitted by the base unit may be received by an antenna on the wireless article, or RF transmissions transmitted by the wireless article by an antenna thereon may be received by the base unit, or RF transmissions by each of the wireless article and the base unit may be received by the other one thereof.
RFID tags are categorized as either active or passive. Active RFID tags are powered by an internal battery and are typically read/write, i.e., tag data can be rewritten and/or modified. An active tag's memory size varies according to application requirements. Passive RFID tags operate without a separate external power source and obtain operating power generated from the reader.
The significant advantage of all types of RFID systems is the noncontact, non-line-of-sight nature of the technology. Tags can be read through a variety of substances such as snow, fog, ice, paint, crusted grime, and other visually and environmentally challenging conditions, where barcodes or other optically read technologies would be useless.
In each case, the RF signals either received or transmitted by the wireless article are received or transmitted by an antenna thereon. Because wireless articles are usually desired to be small in size, the antenna thereon is also small in size. The conductive coil pattern of the RF antenna allows the antenna to receive and radiate energies in the radio frequency range. The sensitivity of the antenna to small amplitude RF signals and the amplitude of the RF signals transmitted by the antenna are a direct function of the area enclosed by the antenna loop and the number of turns of the conductor forming the loop. For a small tag or badge, the size limits the area that an antenna loop can enclose, thereby limiting the RF performance of the antenna. Typically, the antenna is optimized to transmit and receive energy in a relatively narrow portion of the radio frequency range. Often, the radio frequency antenna is connected to an integrated circuit. The integrated circuit receives energy from a detector unit, modulates the energy with an identification pattern stored in the integrated circuit, and then retransmits the modulated energy to the detector unit. RF identification tags typically operate in the frequency range of 100 KHz to 3 GHz, or higher.
Various methods of assembling wireless articles and of forming RF antennae and circuitry on such articles are described in the prior art.
U.S. Pat. No. 6,333,721 to Altwassen, the subject matter of which is herein incorporated by reference in its entirety, describes a method of forming an RF antenna by stamping a conductive coil out of a sheet of metal. The drawback of this method is that the production of the metal coil may result in a large amount of scrap metal. In addition, the RF antennae produced by stamping from a sheet of metal may be less flexible than desired for many applications.
Another way that has been suggested for forming RF antennae is to use strip-back techniques that are commonly used in printed circuit board fabrication. In printed circuit board fabrication, a layer of conductive material, i.e., metal, is formed on top of the substrate and the areas not used for the antenna are stripped away. This method tends to be wasteful when used to produce radio frequency antennae, because the radio frequency coil antenna tends to cover only about 10% of the surface area of the substrate. In contrast, typical printed circuit board implementations require coverage areas of about 70-80%.
Still another way of forming RF antennae on non-conductive substrates is described in U.S. Pat. No. 6,662,430 to Brady et al., the subject matter of which is herein incorporated by reference in its entirety, wherein electrical circuitry is connected to an antenna, which is made of a composite material, and the composite material is connected to electrical circuitry at points. The antenna is made by screening a paste of metal powder, polymer material, and solvent through a screen onto a substrate. While the paste is still wet, the electrical circuitry is bonded to the material by contacting electrical contacts of the electrical circuitry with the wet paste, and then driving off the solvent and/or curing the polymer matrix material.
WO 01/69717 to RCD Technology, Inc., the subject matter of which is herein incorporated by reference in its entirety, describes a process of forming RF antennae using conductive inks. The conductive ink is printed in a RF antenna coil pattern on top of the substrate, and is then cured. The printed antennae may then be used as is or electrodes may be attached to the conductive ink pattern and a metal layer then electroplated on top of the conductive ink pattern.
A fundamental problem with RF tags and identification devices is that the cost of the tag/card must be reduced to a level small compared to the cost of the product to which the tag is attached, which will then allow many more tags to be used and so that high volume production can cut the costs even further. The cost of the tags is the cost of the semiconductor chip, the antenna, the substrate supporting the antenna and chip, and the attachment cost. As the use such devices becomes more and more widespread, there remains a need in the art for greater efficiency in the process while reducing the cost of production.
The inventors of the present invention have discovered that antennae and circuitry may advantageously be produced by using a novel catalytic ink formulation for forming the antennae and circuitry, which may then be plated with an electroless plating composition followed by an electrolytic plating composition.
While catalytic ink formulations and plating catalysts have been widely disclosed in the prior art, there remains a need in the art for improved catalytic ink formulations that can be used for forming RF antennae and phone card circuitry.
U.S. Pat. No. 3,414,427 to Levy, the subject matter of which is herein incorporated by reference in its entirety, describes a method of catalyzing a surface of a material to be plated by a chemical reduction plating process. The method uses a catalyst comprising a complex of palladium chloride dissolved in an organic solvent (i.e., acetone). However the catalyst is not very effective in catalyzing non-conductive (plastic) substrates.
U.S. Pat. No. 4,368,281 to Brummett et al., the subject matter of which is herein incorporated by reference in its entirety, describe a process for making flexible printed circuits on flexible substrates. Brummett et al. describe an ink formulation comprising an appropriate coordination complex of palladium. This complex is depicted by a formula LmPdXn, wherein L is a ligand or unsaturated organic group, Pd is a palladium metal base of the complex, X is a halide, alkyl group, or bidentate ligand and m and n are integers wherein m is from 1 to 4 and n is from 0 to 3. However, there is no suggestion that the catalytic ink formulation described by Brummett et al. can be used for forming RF antennae and circuitry for wireless articles.
U.S. Pat. No. 5,288,313 to Portner, the subject matter of which is herein incorporated by reference in its entirety, describes a plating catalyst that comprises a mixture of catalytic particles dispersed in a liquid coating composition, and is useful for the formation of selectively deposited metal coatings. The catalytic particles are formed from a reduced metal salt that is an electroless plating catalyst coated on an inert particulate carrier. The process of the invention permits plating at a good plating rate and results in a deposit that is and remains strongly adhered to its underlying substrate during prolonged use. However, the catalyst must be applied as a paste and the process further requires a step of solvating (i.e., softening) the non-conductive substrate prior to application of the catalyst.
U.S. Pat. No. 5,378,268 to Wolf et al., the subject matter of which is herein incorporated by reference in its entirety, describes a primer composition for chemical metallization of substrate surfaces without the necessity of prior etching with an oxidant. The primer composition comprises a) a film former based on a polyurethane system; b) an additive having a specific surface tension; c) an ionic and/or colloidal noble metal or organometallic covalent compound thereof; d) a filler; and e) a solvent. However, there is no suggestion that the primer described by Wolf et al. can be selectively applied to produce RF antennae or smart card circuitry.
U.S. Pat. No. 6,461,678 to Chen et al., the subject matter of which is herein incorporated by reference in its entirety also describes a process for applying a catalyst solution comprising a solvent, a carrier, and metal catalyst ions to the surface of a substrate. The catalyst solution can cover then entire surface of the substrate or can be selectively applied to only a portion of a surface of substrate. The concentration of solvent in the layer of catalyst solution on the surface of substrate can be reduced by heating the substrate. Metallic clusters can be formed in the remaining catalyst layer by further heating the substrate. Electroless plating can then deposit metal onto the portion of the surface of substrate coated with the catalyst solution. Electrolytic plating can then deposit additional metal onto the portion of the surface of substrate coated with the catalyst solution. However, Chen et al. also do not suggest that the catalyst described in their invention can be used in a process to produce RF antennae or smart card circuitry.
Thus, there remains a need in the art for an improved catalytic ink composition and for an improved process of using the catalytic ink composition to produce RF antennae and circuitry for wireless articles that overcomes many of the drawbacks of the prior art.